Unless you hold a First Degree RF Wizard rating, chances are good that coax stubs seem a bit baffling to you. They look for all the world like short circuits or open circuits, and yet work their magic and act to match feedline impedances or even as bandpass filters. Pretty interesting behavior from a little piece of coaxial cable.

If you’ve ever wondered how stub filters do their thing, [Fesz] has you covered. His latest video concentrates on practical filters made from quarter-wavelength and half-wavelength stubs. Starting with LTspice simulations, he walks through the different behaviors of open-circuit and short-circuit stubs, as well as what happens when multiple stubs are added to the same feedline. He also covers a nifty online calculator that makes it easy to come up with stub lengths based on things like the velocity factor and characteristic impedance of the coax.

It’s never just about simulations with [Fesz], though, so he presents a real-world stub filter for FM broadcast signals on the 2-meter amateur radio band. The final design required multiple stubs to get 30 dB of attenuation from 88 MHz to 108 MHz, and the filter seemed fairly sensitive to the physical position of the stubs relative to each other. Also, the filter needed a little LC matching circuit to move the passband frequency to the center of the 2-meter band. All the details are in the video below.

It’s pretty cool to see what can be accomplished with just a couple of offcuts of coax. Plus, getting some of the theory behind those funny little features on PCBs that handle microwave frequencies is a nice bonus. This microwave frequency doubler is a nice example of what stubs can do.

youtube.com/embed/tQnCpV4L_6s?…

3D printing metal has been somewhat of a holy grail for the last decade in the hobby 3DP scene. We’ve seen a number of solutions, including using expensive filaments that incorporate metal into the usual plastic. In parallel, we’ve seen ceramic printers, and paste printers in general, coming into their own. What if you combined the two?

You’d get [Leah Buechly] et al’s CeraMetal process, which is the cheapest and most straightforward metal printing method we’ve seen to date. It all starts off with a custom bronze metal clay, made up of 100 g bronze powder, 0.17 g methyl cellulose, 0.33 g xanthan gum, and 9 g water. The water is fine-tuned to get the right consistency, and then it’s extruded and sintered.

The printer in question is an off-the-shelf ceramic printer that appears to use a pressurized clay feed into an augur, and prints on a linen bed. [Leah] had to write a custom slicer firmware that essentially runs in vase mode but incorporates infill as well, because the stop-start of normal slicers wreaked havoc with clay printing.

The part is then buried in activated carbon for support, and fired in a kiln. The result is a 3D printed bronze part on the cheap; the material cost is essentially just the cost of the metal powder and your effort.

We had never heard of metal clay before, but apparently jewelers have been using it for metals other than just bronze. The Metal Clay Academy, from the references section of the paper, is an amazing resource if you want to recreate this at home.

Paste printers are sounding more and more interesting. Obvious applications include printing chocolate and printing pancakes, but now that we’re talking metal parts with reasonably consistent shrinkage, they’ve got our attention.

When monitors around the world display a “Blue Screen of Death” and you know it’s probably your fault, it’s got to be a terrible, horrible, no good, very bad day at work. That’s likely the situation inside CrowdStrike this weekend, as engineers at the cybersecurity provider struggle to recover from an update rollout that went very, very badly indeed. The rollout, which affected enterprise-level Windows 10 and 11 hosts running their flagship Falcon Sensor product, resulted in machines going into a boot loop or just dropping into restore mode, leaving hapless millions to stare at the dreaded BSOD screen on everything from POS terminals to transit ticketing systems.

Tales of woe from the fallout from what’s being called “the largest IT outage in history” are pouring in, including this very bewildered game developer who while stranded at an airport had plenty of ponder about why CrowdStrike broke the cardinal rule of software development by rolling a change to production on a Friday. The good news is that there’s a workaround, but the bad news is that someone has to access each borked machine and manually delete a file to fix it. Current estimates place the number of affected machines at 8.5 million, so that’s a lot of legwork. There’s plenty of time after the fix is rolled out for a full accounting of the impact, including the search for the guilty and persecution of the innocent, but for now, let’s spare a moment’s pity for the devs who must be sweating things out this weekend.

Back in 2011, Craig Fugate of the Federal Emergency Management Agency said of disaster response in the southern US, “If you get there and the Waffle House is closed? That’s really bad.” Thus was born the “Waffle House Index,” an informal measure of a natural disaster’s impact based on where individual restaurants in the chain that prides itself on always being open are actually up and running. With over 1,900 locations in 25 states, you’d think it would cover just about any emergency, but desperate Texans eschewed the index during the recent extensive power outages in the Houston area caused by Hurricane Beryl by inventing the “Whattaburger Index.” We haven’t had the pleasure of this particular delicacy, but it seems Texans can’t get enough of the hamburger chain, enough so that their online app’s location map provides a pretty granular view of a wide swathe of Texas. Plus, the chain thoughtfully color-codes each location’s marker by whether it’s currently open or closed, making it a quick and easy way to check where the power is on or off — at least during regular business hours. Hat’s off to the enterprising Texans who figured this out, and here’s hoping that life has returned to normal for everyone by now.

While we’re generally not fans of Apple products, which seem overpriced and far too tightly controlled for our liking, we’ve been pretty impressed by some of the results people have reported using their Apple AirTags to recover lost or stolen items — this recent discovery of a cache of stolen tools (fourth item) comes to mind. Results such as that require a “me too” response from the Android side of the market, resulting in the Find My Device network that, perhaps unsurprisingly, doesn’t appear to work very well. The test was pretty much what you’d expect — drop an Android-compatible tag in the mail along with an AirTag and track their journey. The Android tag only reported in a couple of times, while the AirTag provided a comprehensive track of the parcel’s journey through the USPS. Our first thought is that this speaks mostly to the power of being first to market, allowing Apple to have a more completely built-out infrastructure. But this may say more about the previously mentioned flexibility of Android compared to Apple; we know we noped the hell out of participating in Find My Device as soon as it rolled out on our Android phone. Seems like a lot of Android users feel the same way.

And finally, while we haven’t checked out comments on this week’s podcast, we’re pretty sure we’re getting raked over the coals for betraying our ignorance of and lack of appreciation for the finer points of soccer, or football. Whatever you call it, we just don’t get it, but we do understand and agree with our own Lewin Day’s argument that instrument-enhanced officiating isn’t making the game any better. Our argument is that in any sport, the officials are like a third team, one that’s adversarial to both of the competing teams, hopefully equally so, and that giving them super-human abilities isn’t fair to the un-enhanced players on the field/pitch/court/ice. So it was with considerable dismay that we learned that Major League Baseball is experimenting with automatic umpires to call balls and strikes behind the plate. While you may not care about baseball, you have to appreciate the ability of an umpire to stand directly in the line of fire of someone who can hurl a ball fast enough to hit a strike zone about the size of a pizza box the ball in less than 500 milliseconds. Being able to determine if the ball ended up in or out of that box is pretty amazing, not to mention all the other things an umpire has to do to make sure the game is played by the rules. They’re not perfect, of course, and neither are the players, and half the fun of watching sports for us is witnessing the very human contest of wills and skills of everyone involved. It seems like a bad idea to take the humans out of that particular loop.

An annoying fridge that beeps incessantly when the door is open too long should be an easy enough thing to fix by disconnecting the speaker, but when as with [kennedn]’s model it’s plumbed in and the speaker is inaccessible, what’s to be done? The answer: create a mod chip for a fridge.

While the fridge electronics themselves couldn’t be reached, there was full access to a daughterboard with the fridge controls. It should be easy enough to use them to turn off the alarm, but first a little reverse engineering was required. It used a serial communication with an old-school set of shift registers rather than a microcontroller, but it soon became apparent that the job could be done by simply pulling the buttons down. In a move that should gladden the heart of all Hackaday readers then, the modchip in question didn’t even have to be a processor, instead it could be the venerable 555 timer. Our lives are complete, and the fridge is no longer annoying.

The 555 is unashamedly a Hackaday cliche, but even after five decades it still bears some understanding.

We’ve all been there — you forgot your lunch, but there are AC outlets galore. Wouldn’t it be so much simpler if you could just plug in like your phone? Don’t try it yet, but biologists have taken us one step further to being able to fuel ourselves on those sweet, sweet electrons.

Using an “electrobiological module” of 3-4 enzymes, the amusingly named AAA (acid/aldehyde ATP) cycle regenerates ATP in biological systems directly from electricity. The process takes place at -0.6 V vs a standard hydrogen electrode (SHE), and is compatible with biological transcription/translation processes like “RNA and protein synthesis from DNA.”

The process isn’t dependent on any membranes to foul or more complicated sets of enzymes making it ideal for in vitro synthetic biology since you don’t have to worry about keeping as many components in an ideal environment. We’re particularly interested in how this might apply to DNA computing which we keep being promised will someday be the best thing since the transistor.

Maybe in the future we’ll all jack in instead of eating our daily food pill? If this all seems like something you’ve heard of before, but in reverse, maybe you’re thinking of microbial fuel cells.

Su basta!, un media indipendente francese, c’è un interessante articolo che presenta l’esperienza delle “banche del tempo libero“ (Fritidsbanken), in particolare la sede di Malmoe, nel sud della Svezia: basta.media/Suede-recycleries-…

La sede si trova in un centro commerciale eha l’aspetto di un normale negozio di articoli sportivi, ma lì sci, pattini in linea, racchette da tennis, palloni, tende e altri articoli sportivi sono di seconda mano e non si vendono, ma si prestano gratuitamente per due settimane, basta lasciare il proprio nome e il proprio numero di telefono.
Nella sede di Malmoe c’è spazio anche per accese partite ai due tavoli da ping pong e non mancano le attività per la riparazione delle attrezzature, secondo la responsabile al momento nel negozio si prestano circa 150 oggetti al giorno, d’inverno, il doppio.

L’associazione delle Fritidsbanken è nata nel 2013 ed ora è diffusa in molti centri del paese, ha come scopo dare nuova vita ad attrezzature sportive usate, prestandole gratuitamente per promuovere l'attività sportiva e all'aria aperta. Le “banche del tempo libero” vengono finanziate dalle amministrazioni locali da associazioni per la promozione dello sport, da fondazioni e da alcune regioni.

L’associazione ha un suo sito con una versione anche in inglese dove spiega che cosa sono e come funzionano le Fritidsbanken: fritidsbanken.se/en/how-it-wor…

Un grand merci, un grosso grazie a @Basta! per la segnalazione di questa bella iniziativa.
#EconomiaCircolare #biblioteche #Svezia #sport #ambiente #condivisione #BancheDelTempoLibero @macfranc

tl;dr
Per sapere di più su di me: dmi.unict.it/nfarceri?page=com…

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